1. Field of the Invention
This invention relates to a method of compressing radiation signals by conducting redundancy suppression encoding processing such as prediction encoding processing of the radiation image signals.
2. Description of the Prior Art
Image signals representing half tone images, such as television signals, are composed of enormous amounts of information, and a broad-band transmission line is required for transmission of the image signals. Such image signals involve much redundancy, and various attempts have been made to compress the image signals by suppressing the redundancy. Also, in recent years, recording of half tone images on optical disks, magnetic disks, or the like has been put into general practice. In this case, image signal compression is conducted generally for the purpose of efficiently recording image signals on a recording medium.
In a radiation image recording and reproducing system wherein a stimulable phosphor sheet is used as disclosed in, for example, U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, a radiation image of an object such as the human body stored on the stimulable phosphor sheet is read out to obtain digital image signals, which are then subjected to appropriate image processing and used for reproducing the radiation image as a visible image on a cathode ray tube (CRT) or the like. After the visible image is reproduced, the processed digital image signals may be stored on a recording medium such as an optical disk, and read out of the recording medium when necessary for reproducing the visible image.
However, since the aforesaid radiation image is generally a half tone image, the amount of digital image signals representing the radiation image is very large. Therefore, in a large-scale hospital or the like where, for example, hundreds or thousands of radiation images are to be recorded annually, the amount of image signals which should be stored becomes enormous in the case where all of the image signals representing the recorded radiation images are to be stored. A large space is required for storing the image signals and the cost of storing the image signals becomes very high. Accordingly, a need exists for a technique of compressing the image signals as efficiently as possible before storing the image signals. This applied also to the case of transmission of the radiation image signals.
The need for compressing the image signals with a high efficiency when storing or transmitting the digital image signals exists not only in the case of the radiation images recorded by use of the aforesaid radiation image recording and reproducing system but also in the cases of radiation images recorded by various other methods.
On the other hand, there has heretofore been known a technique wherein redundancy of the digital image signals is suppressed by redundancy suppression encoding processing such as prediction encoding, thereby compressing the amount of the image signals, and thereafter the compressed image signals are stored or transmitted.
Accordingly, the signal compression technique may be utilized in the course of storing or transmitting the digital image signals representing a radiation image. In this case, the compressibility should be as high as possible. Therefore, it is desired that the signal compression technique be utilized to obtain as high a compressibility as is practicable for maintaining the necessary image quality of a reproduced visible image.